1. Field
Embodiments of the present invention relate to a hydraulic brake device and a method for controlling the same.
2. Description of the Related Art
Hybrid vehicles and electric vehicles are next-generation environmentally friendly vehicles, which include an engine, in particular, an internal combustion engine, and a motor to be driven by electrical energy stored in a battery. Such a vehicle travels through driving of the engine and motor.
In a hybrid vehicle or an electric vehicle, braking is carried out through control of hydraulic pressure of a master cylinder or control of a motor. In order to achieve an enhancement in braking performance in such a vehicle, a booster or active hydraulic boost (AHB) is used.
The AHB is a device to generate a braking force corresponding to a pedal force exerted by a driver by directly supplying a brake fluid charged under high pressure to a booster. The AHB includes a brake actuation unit having a pedal simulator and a master cylinder, and a hydraulic power unit.
The pedal simulator generates reaction force corresponding to a pedal force from the brake pedal depressed by the driver. The hydraulic power unit is charged with a brake fluid under high pressure. In response to the pedal force from the brake pedal, the hydraulic power unit supplies pressure corresponding to the pedal force to the booster, to enable the master cylinder to generate a sufficient pressure.
That is, when the brake pedal is depressed by the driver, the active hydraulic booster supplies the pressure generated from the master cylinder to wheel cylinders. As a result, the wheel cylinders generate braking force, using the pressure supplied form the master cylinder.
The hydraulic power unit is equipped with a pressure sensor to sense a pressure supplied from a high pressure accumulator to a hydraulic pressure controller. A control unit performs a control operation, based on the pressure sensed by the pressure sensor and a target pressure.
That is, the control unit determines a braking degree by detecting a pedal force from the brake pedal depressed by the user, and sets the determined braking degree as a target pressure. Based on the target pressure, the control unit controls a valve included in the hydraulic power unit. The pressure generated in accordance with control of the valve is detected by a pressure sensor included in the hydraulic power unit.
If the output value from the pressure sensor included in the hydraulic power unit is fixed to a value in the vicinity of 0 bar due to failure of the pressure sensor, the pressure difference between the pressure detected by the pressure sensor and the target pressure is continuously generated. As a result, the control unit controls the valve to be opened at an increased opening degree or to be more frequently opened.
In this case, the pressure charged in the hydraulic power unit is completely transferred to the wheels. As a result, there may be severe problems such as excessive braking, sudden braking, insufficient braking, abnormal braking sensation and abnormal braking force.